New automatics are definitely improved, and some like the Porsche PDK are fantastic.
Older ones like the GM 4L60 in my Tahoe and other GM cars, and used up until just a few years ago, were not so great for 'spirited' driving.
Those never pre-emptively downshifted as the rpms dropped, for example when slowing for a corner. When accelerating out of the corner, or trying to pass someone, it is always in too tall a gear and very reluctant to downshift (at least in my Tahoe). It makes it feel sluggish all the time.
I keep reading of overheating issues on the track and torque converter failures with the 8 speed auto in the Corvette. Plus the active fuel management (cylinder deactivation) can't be disabled if you have an auto, while it can with the manual. If I were in the market for a new Corvette, I would choose a manual for those reasons alone.